This invention relates to a metal casting (or molding) device for forming a cast product having an undercut.
Heretofore, in preparing a product having an undercut (inner cut-out configuration) by die casting (die cast molding), it has been necessary to use a collapsible core, such as a salt core, at the time of die casting, or to apply post-processing, such as cutting off unneeded bulk portions from a die cast product. However, these conventional techniques suffer from a drawback such as increased cost or an increased number of steps. Thus, in JP Patent Kokai JP-P2000-24769A, for example, a die casting method has been proposed in which an ejection member (movable core member) operating in association with an ejection pin is used to form an undercut simultaneously with molding.
In the die casting method, disclosed in the publication of JP Patent Kokai JP-P2000-24769A, an ejection member for forming an undercut is provided in a portion (inner portion) of a movable core (that is a core loaded on a movable die). This ejection member is adapted to be movable along a direction of ejection of an ejection pin, that is, in the horizontal direction. Using the movable core and the ejection member as one unit, a cast product presenting an undercut is formed in a cavity provided between the fixed die and the movable die. In taking out the cast product out of the metal die device, the dies are first opened, and the ejection member and the ejection pin are then pushed out towards a fixed die to disengage the cast product and a runner continuing thereto momentarily from the movable die and the movable core. Then, the runner is gripped by a robot catch and the cast product and moved in a transverse direction (in a direction perpendicular to the direction of movement of the movable die, that is, in a vertical direction) along with the runner to disengage the cast product ultimately from the ejection member.
However, the above-identified die casting method, disclosed in JP Patent Kokai JP-P2000-24769A, has a number of deficiencies. First, it is necessary to provide the ejection member, which is movable in the horizontal direction in synchronism with the extruding operations of the ejection pin, within the inside of the movable core. Moreover, since a robot catch mechanism needs to be provided between the fixed and movable dies following the mold opening, the metal die device is of a complex and bulky structure.
Second, in the above-mentioned die casting method, it is mandatory to use a metal die device of such a structure in which an ejection member for forming an undercut is protruded from within the movable core towards the fixed die in synchronism with the extruding operation of the ejection pin provided on the movable die. If this metal die device is used, there is caused no significant inconvenience when such an undercut in the cast product is produced in which the undercut in the cast product is opened towards the movable die. However, if, with the use of the same method and device, such an undercut of the cast product is to be formed which is opened towards the fixed die, with the portion of the cast product subjected to severe shrinkage, that is the portion of the cast product subjected to relatively large rapping resistance upon removal from the die, lying on the fixed die side, such a phenomenon in which the cast product becomes adhered to the fixed die at the time of die opening (so-called sticking) tends to be produced. Should this sticking occur, it becomes difficult to disengage the cast product from the metal die device. In addition, the useful life of the metal die tends to be shortened. That is, in the above-mentioned conventional die casting method, considerable constraint may be imposed on the casting conditions in the metal die device, depending on the position or shape of the undercut in the cast product, with the consequence that the degree of freedom in designing the metal die is reduced.